This invention relates to ultra-wide bandwidth circuits and systems and in particular to a low power CMOS pulse generator device for use in ultra-side bandwidth circuits and systems.
In ultra-wideband (hereinafter referred to as “UWB”) applications, such as communication systems, radar applications, and radio frequency identification tagging, ultra-short pulses are used for transmitting an information signal. UWB applications are emerging as a useful way to provide high speed, low power communications with resistance to multi-path interference. Advantages of UWB systems over conventional radio frequency (hereinafter referred to as “RF”) systems in appropriate applications include low power consumption and simple architecture, as described by Win and Scholtz in IEEE Commun. Lett. Vol 2, No. 2, pp 10-12 (1998), and incorporated herein by reference. UWB signals generally consist of a train of extremely narrow pulses, often on the order of 0.2-2.0 nanoseconds. Because the pulse width is short compared to the pulse period, UWB signals occupy a broad communication band at low power levels.
Federal Communications Commission (hereinafter referred to as “FCC”) regulations for UWB technology require that transmitted UWB pulses should observe strict limitations in terms of a pulse bandwidth and amplitude. The emissions of radio frequency devices generally are regulated by Part 15 of Title 47 of the Code of Federal Regulations (“C.F.R.”). Subpart F, in particular, entitled “Ultra-Wideband Operation,” and found at 47 C.F.R. §§15.501-15.525, recites regulations that specifically restrict the emissions of UWB devices. Among those regulations, the FCC sets forth frequency masks for UWB devices in particular applications, namely “ground penetrating radars and wall imaging systems” (§15.509); “through-wall imaging systems” (§15.510); “surveillance systems” (§15.511); “medical imaging systems” (§15.513); “vehicular radar systems” (§15.515); “indoor UWB systems” (§15.517); and “hand held UWB systems” (§15.519). These frequency masks are incorporated herein by reference. Further limitations and measurement requirements are set forth in §15.519, “Technical requirements applicable to all UWB devices,” also incorporated herein by reference.
Given the tight regulations of UWB devices, designing a simple and low power UWB pulse generator that can meet FCC limits is challenging. The first or second derivative of a Gaussian pulse is generally used for a UWB pulse, because it is easily expressed by a mathematical form. Several methods have been proposed to generate these signals using integrated circuits, and are described by Stoica et al., in Proc. 2004 IEEE Conf. on Ultra Wideband Systems and Tech, pp 258-262 (2004), by Bagga et al., in Proc. 2004 IEEE Conf. on Ultra Wideband Systems and Tech, pp 130-134 (2004), by Gerrits et al., in IEE Electron. Lett., Vol. 38, No. 25, pp 1737-1738 (2002), and by Kim et al., in Proc. 2003 IEEE Conf. on Ultra Wideband Systems and Tech, pp 258-262 (2003), all of these articles being incorporated herein by reference. A disadvantage of these pulse generators is that the output signals generated must further be filtered in order to satisfy FCC regulations. Furthermore, many of these previous approaches consume constant powers for biasing.
Considering the various FCC-imposed frequency masks, the fifth derivative of the Gaussian pulse is in some ways more effective as single UWB pulse than the first or second derivative of the Gaussian, as described by Sheng et al., in Conf. Rec. 2003 IEEE Int. Conf. Communications, pp. 738-743 (2004), incorporated herein by reference. The spectrum of this pulse is close to maximally occupied under the FCC limitation floor, and this pulse can be transmitted without any extra filtering. However, although the fifth-derivative of a Gaussian pulse can be implemented with complicated digital signal processing circuits, such circuits typically consume too much power, which can make these circuits unsuitable for low power applications such as radio frequency identification tagging, as described by Carr et al., in IEEE Commun. Lett., Vol 7, No. 5, pp 219-221 (2003) and incorporated herein by reference, and other applications where power consumption is a concern.
It is generally desirable to design pulse generators with a simple and power efficient architecture, preferably without the need to use additional filtering to meet FCC specifications. It would be advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.